DEPOSITIONAL ENVIRONMENT OF THE MARINE HYDROCARBON SOURCE ROCK IN THE QIANGTANG BASIN, QINGHAI-TIBET PLATEAU

The Qiangtang Basin is the largest Mesozoic marine residual basin in Qinghai-Tibet plateau.The Upper Triassic Formation is sub-abysmal basinal facies deposit in the south and north depressions.A black shale layer developed.The climate in the lower part of Lower and Middle Jurassic Formation is semi-warm and semi-xerothermic to warm and hot.A black neritic to sub-abysmal basinal facies shale layer developed in the southern part of the south depression.In the middle part of Middle Jurassic and the lower part of Upper Jurassic Formation,the scope of transgression increased.Carbonate-rock platform facies deposit is dominant and platform depression is the main place of source rock developing.A littoral to neritic detrital rock deposit is in the upper part of Middle Jurassic Formation.Lagoonal subfacies shale and prodelta subfacies mudstone are the main hydrocarbon sousce rocks.The characterstics of deposition and development of the Mesozoic marine hydrocarbon source rock in Qiangtang basin are similar to the ones in the large carbonate-rock oil and gas fields at home and abroad.Black abysmal to sub-abysmal basinal facies shale,marl and shale depositing in the platform depression and lagoonal subfacies or prodelta subfacies shale and mudstone are the main hydrocarbon source rocks.